Check for allergies especially those caused by foods or items you consume, but here is a recommended way to check and be able to do the testing immediately and by yourself or preferably with another person:

You are so young that it's probably nothing to worry about yet, but learn how to immediately test for food allergies yourself or with a helper by using MRT or muscle response testing. It's easy to learn, but takes a little practice at first and very accurate . . . then you'll know what foods or substances you need to avoid or to treat to eliminate the allergy. My wife and I use these techniques all the time.

Food sensitivities, intolerances, allergies play a bigger role in health than most people realize and they can wreck havoc on your gastro-intestinal tract and that is what I would suspect is starting to happen to you. Of course stress can play a part in this too so if stress is a problem, learn how to release that as much as possible and try not to let it build up.